1. Field of the Invention
The present invention relates to acoustic transducer apparatus and methods for measuring a rate of flow of a fluid through a pipe. More specifically, the invention relates to arrangements in which ultrasonic transducers, mounted in housings, are clamped to an external surface of the pipe.
2. Background Information
Transit time flow meters used to measure the rate of flow of fluids through a pipe commonly employ clamp-on transducers attached against an external surface of the pipe. One of the problems associated with clamp-on transducers is that the transducer housing may move or even become unclamped from the pipe at some time during its installed life. Pipe vibration and operation at extreme temperatures both increase the risk of a mounting failure.
This risk is further increased when the transducer is not mounted either on the top or bottom of a horizontal pipe because of gravitational forces tending to make the transducer fall off the pipe. Sometimes these angled mounting arrangements are selected because of physical access considerations. In other installations a transducer is mounted at some angle away from the top of the pipe to avoid the ultrasonic beam having to contend with air or gas bubbles.
Regardless of the clamping method used to hold a transducer against a pipe, the risk of mounting failure increases with increasing weight of the transducer and its housing. Thus, there is a need for transducer housings having a minimum realizable density.
Current art clamp-on transducers commonly employ liquid or gel acoustic coupling promoters, such as silicone greases. Because these coupling promoters tend to evaporate, wick away or otherwise degrade or leave the area over a period of time, the transducer mounting may require frequent maintenance. Thus there is a need for improvement in materials selected for coupling a transducer to a pipe.